Articulated mobile conveyors are used for various purposes, such as in mining, or in agricultural harvesting. For example, the conveyors can be used for excavating, stacking, or reclaiming material such as ore, coal, granite, clay, salt, potash, or other bulk material. Certain mobile conveyor systems are made up of a plurality of articulated sections or segments. The sections are joined to one another using, for example, ball joints. This enables rotational translation of one section relative to another in view of grade changes in the ground over which the sections lie. This also provides flexibility between segments when the conveyor is moved. Each section supports an endless loop belt which transports material over the length of the entire conveyor. Each section of the conveyor is separately movable relative to the ground and includes, for example, tracks or wheels in contact with the ground below the section, typically located at the end of the section. Each section typically has a dedicated drive unit for moving the section relative to the ground, the drive unit typically being independently steerable and operable to allow one section to be moved relative to an adjacent section. Thus, the entire conveyor can be moved or transported by activating a plurality of the drive units simultaneously. Such may be done for example when it is desired to harvest or mine in a different location, or when it is desired to transversely move the conveyor as material is stripped away from the surface of the earth or is moved from large storage piles. For examples of such articulated mobile conveyor, see the following patents which are incorporated herein by reference: U.S. Pat. Nos. 4,206,840 to Hanson; 4,031,997 to Nelson; and 3,361,248 to Daymon.
If While moving the conveyor relative to the ground, it may be desirable to longitudinally align two or more adjacent sections. See, for example, U.S. Pat. No. 3,422,949 to Bankauf (incorporated herein by reference). Bankauf discloses a guide follower which, upon too much misalignment, activates a hydraulic system to cause steerable wheels to turn. If left uncorrected, misalignment may cause the continuous belt or the tripper (used to transfer material from the belt to a secondary belt) to disengage from the conveyor assembly.
After moving the conveyor, it may be desirable to align two or more adjacent sections relative to one another such that the endless belt extends along a straight line in a common vertical plane, such as for better belt training from one section to the next. Some alignment mechanisms employ a series of pulleys and cables connected to each adjoining section for determining when precise longitudinal alignment has been reached. U.S. Pat. No. 3,897,640 to Swisher, Jr. et al. (incorporated herein by reference) discloses a conveyor including an alignment switch and a sensor connected to the alignment switch for correctingly moving the conveyor to maintain the position of the conveyor at a predetermined alignment position.
One alignment system, which is an improvement over such systems involving pulleys and cables, is described in U.S. patent application Ser. No. 08/508,125, filed Jul. 27, 1995, titled "Mobile Conveyor Including Alignment System" assigned to the assignee hereof and incorporated herein by reference.
Multi-segmented conveyor systems are typically aligned using the endpoints of the conveyor system as reference points. Thus, when segments intermediate the endpoints fall out of alignment in a direction opposite to the direction of travel, they need to "catch up" to the rest of the conveyor system to be brought back into alignment. In order to insure that there would always be some additional capacity to allow such segments to "catch up" to the endpoints, the transmissions or "transfer boxes" at the endpoints would be geared such that the endpoints could never travel faster than the overall system design. The system design speed would thus be available only to the intermediate segments to allow them to "catch up" to the rest of the conveyor system. This is undesirable since the conveyor system would never be able to travel overland at its true design capability.
It is thus desirable to provide an alignment system having increased accuracy over prior art systems, and which does not impose constant velocity constraints on the conveyor system.